Iron deficiency anemia is the common problem during pregnancy. Detection of iron deficiency early during pregnancy can reduce maternal and child mortality and morbidity. Red cell distribution width is a new routine parameter in fully automated hematology analyzer that can give the idea of early iron deficiency before other test. It gives the idea of red cell size variation which is the earliest morphologic changes in iron deficiency anemia. In prelatent and latent stage of iron deficiency MCV are normal. Whereas in latent stage Red Cell Distribution Width (RDW) would be expected to increase because of a microcytic population of cells appears in the blood. This study evaluates the role of red cell distribution width and RBC indices in determining iron deficiency early and provide reliable and useful technique. In this study 190 pregnant women were included. RDW, MCV, MCH, MCHC and iron profile were done. RDW compared with MCV, MCH and MCHC in various stages of iron deficiency. In latent stage of iron deficiency higher RDW was found significant than MCV, MCH, MCHC (p<0.05). In this study RDW had sensitivity 82.3% and specificity 97.4%. Whereas MCV, MCH and MCHC had 29.2%, 68.1% and 15% sensitivity but specificity was 98.7%, 83.1% and 96.1% in the detection of iron deficiency. Iron deficiency anaemia without other complicating disease could be screened out early by increased RDW when RBC indices were normal.